1. Field of the Invention
The present invention relates to a multiple-terminal communication system, and more particularly, to a multiple-terminal communication system for realizing radio communication between a plurality of radio terminal equipment such as personal computers.
2. Description of the Related Art
Recently, two-way communication is frequently carried out between a plurality of terminal equipment such as personal computers. The two-way communication with personal computers can realize a teleconference. Under these circumstances, it is required to provide a multiple-terminal communication system that can smoothly and correctly communicate data between the personal computers (terminal equipment).
Further, data communication between terminal equipments such as personal computers is carried out through a wired network such as a LAN (Local Area Network), or a radio network. In any case, each terminal equipment unit must have transmission and reception frequencies, so that the number of frequency channels required for terminal communications will be at least twice the number of the terminal equipment. To form a teleconference system with terminal equipment such as personal computers, RS-232C interfaces are usually employed. Further, a module (a radio control module) may be attached to the RS-232C interface of a communication terminal equipment unit such as a personal computer, to provide the terminal equipment unit with a radio communication function.
Generally, a pair of such radio communication terminals carries out full-duplex communication with the use of two different frequencies because the RS-232C interface is constituted for one-to-one communication. In an exceptional case, however, a specific terminal may be used exclusively as a transmission terminal, and another or more terminals as reception-only terminals, to carry out one-way communication without interface control. This may be the case of a broadcasting station that transmits information to many domestic receivers. In this case, each receiver cannot transmit data because it will be uncontrollable if a plurality of receivers simultaneously transmit data.
As described above, the conventional wired technique such as the LAN for communicating data between terminal equipment requires enormous costs for laying circuits and cables for connecting the equipment. This is the reason why the wired technique is not widely used. Further, on the other hand, the conventional wireless technique for communicating data between terminal equipment requires, for example, radio frequency channels of more than twice the number of the terminal equipment units. In addition, the number of the terminal equipment is not easily expanded because frequencies handled by a repeater are limited. Since usable radio frequencies are limited, it is not economical to employ many frequencies for communications within one group.